The “electric grid” can be described in terms of its most basic elements as a collection of generation, transmission, and distribution systems. Transmission utilities transport energy from generators to end-user distribution systems over high-voltage transmission lines. Power is dispatched from the generators and distributed among transmission lines based in part on capacity ratings of the transmission line.
The transmission line (also referred to herein as “the conductor” or “the line”) has an ampere carrying capacity (“ampacity”) rating that is constrained by two limits: (1) the conductor's position relative to the tower attachment points (“sag”) and (2) the maximum design temperature of the conductor material.
The amount of sag is directly related to the amount of current the conductor carries and hence to its temperature; if there is too much current and too high of a temperature, there is a risk of too much sag. Utilities must limit the amount of sag to prevent arcing from the conductor to objects or the ground. If the maximum conductor design temperature is exceeded permanent deformation of the conductor (e.g., inelastic elongation or expansion) occurs.
In addition to the amount of current the conductor is carrying, the temperature of a transmission line is also greatly affected by wind against the line. This of course, can vary greatly along the route of the line, making it difficult to discern the actual temperature variation along the line. Conventionally, to stay within temperature constraints, it is not expected to know the actual temperature distribution along the transmission line. The maximum current load is set as a compromise between an estimation of temperature conditions and risk minimization.
More recently, attempts have been made to provide real time temperature monitoring along the transmission line. Various types of sensors have been used to directly measure temperature on the transmission line. The object of temperature monitoring is to better achieve power distribution according to the actual capacity of the transmission line.